


an ace up your sleeve

by Cynder713



Category: Supernatural
Genre: (apparent) mind control, Asexual Castiel (Supernatural), Asexual Character, Asexuality, Canon-Typical Violence, M/M, Pre-Slash, Sirens
Language: English
Status: Completed
Published: 2017-05-14
Updated: 2017-05-14
Packaged: 2018-10-31 12:54:57
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 7,271
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10899768
Author URL: https://archiveofourown.org/users/Cynder713/pseuds/Cynder713
Summary: Cas, determined to prove that he can take the lead on a hunt, brings a case to the boys. It's a siren, of course it's a siren, and despite Dean's protests they take it, with Cas offering to play the bait.





	an ace up your sleeve

**Author's Note:**

> Thanks to weasleychick32 for betaing for me, and for catching all my weird Aussie slang that I didn't even realise was slang. This fic is infinitely better because of you! All remaining mistakes are mine, naturally.  
> And a huge thankyou to kuwlshadow for the amazing art! You picked such a good moment to bring to life and I'm just so honoured to have such lovely art be drawn for my little fic!

 

 

“I’ve found a case.”

Dean looked up from the article he was reading – it was either about a fairy gone rogue in West Virginia and terrorising the locals, or Mothman was one of the supernatural creatures that was less of a hoax than most cryptid sightings were - to meet Cas’ expectant gaze.

“You’ve found a case?”

“Yes.”

“When were you even looking for a case?”

Cas sat down next to Dean and took over his laptop, calling up a news website. “I’ve been looking for some time now for something that could serve as - you would probably call it a ‘trial run’.”

Dean raised his eyebrows, holding back a grin. “Oh? Is that right?”

Cas shot Dean a bemused look. “Yes, Dean. Seeing as I am the one who has been doing the research, I am fairly sure I am accurate- oh, I see, you’re making fun of me.”

Dean laughed, then laughed harder when Cas’ expression became exasperated. “No, no I’m not laughing at you - well, I am, but it’s not a bad thing it’s just-” Dean cut himself off before he could actually call the righteous, angel, warrior of god Castiel ‘cute’.

Dean cleared his throat. “Seriously though, not makin’ fun of you, it’s just funny when you take things so literal. Reminds me that you’re still… you.”

Cas smiled that little smile of his when he got the inside joke. _Cursed or not…_

Dean blinked and looked down at his laptop to break the mood, realised that Cas had stolen it, and finally got around to remembering why Cas had come over to him in the first place. He’d had something important to talk about, a case, he hadn’t just come over here to, what, to flirt?

Dean berated himself and tried for a smooth recovery. “So, uh, Cas...tiel. You found a, uh, case? For us to do? Us, being, you me and Sam, obviously, ‘cause that’s how it normally works, right?”

Yeah, nailed it.

Cas nodded and turned the laptop back to face Dean. The browser was open to a news report about a man who murdered his wife with a kitchen knife and immediately turned himself in after the fact.

“Huh,” said Dean. “Little weird I guess. Could be a possession.”

“I’d considered that, but what would a demon gain from making a man kill his wife and releasing him? No, there is a more likely suspect.”

Dean sighed. “So then you’re thinking…”

Cas nodded. “A siren, yes.”

Dean closed his eyes wearily. “Ahhh yep. Man, I was hoping you wouldn’t say that. Ok then, sunshine, what’s the pitch?”

Cas narrowed his eyes. “Is this another sports metaphor?”

Dean laughed, his bad mood at the idea of another siren case lifting at the sight of Cas’ sincere confusion. “No, I meant like, sell me on your plan. What is it exactly that you wanna do?”

“Oh, of course.” Cas scrolled down the page and leaned forwards intently. “This man lives in Salina. It’s only an hour or so drive from the bunker and the case is clear cut. You and Sam have dealt with a siren before-“ Cas ploughed right on past Dean's uncomfortable expression, “-and I believe I already have a good lead on where its hunting ground is. This is as simple a case we are going to get that isn’t a salt and burn, and I would like to take lead.”

Dean squirmed a bit under Cas’ insistent gaze. “Cas.”

“Dean.”

“… are you sure about this?”

Cas rolled his eyes and leaned back as Dean ploughed on with a hurried explanation.

“It’s just that, and I’m not saying I don’t think you’re ready to take the lead, but me and Sam have been doing this way longer than you have-“

“Dean, I am older than this earth.”

“-and you don’t really know our MO, this could end up with all of us clashing heads and we both know that’s no way to run an operation-“

“I have been commanding armies for longer than the language you speak has existed.”

“-plus, you know, sirens aren’t exactly a rookie target, why don’t we just wait until something easier comes along?”

Cas sighed. “I thought you’d bring that up.”

“What?”

“Dean, I know your previous encounters with sirens haven’t been pleasant.”

“Yeah, no shit!”

“But I am confident in my abilities to face such a creature, more so than I am in your ability.”

Dean looked taken aback. “And what the hell is that supposed to mean?”

“Don’t get distracted by that, Dean. You’re just trying to talk me out of taking this case.”

“Hell yeah I’m trying to talk you out of taking this case! If I go back to purgatory and still never see another siren again, it’ll be too soon!”

“That doesn’t make sense.”

Dean shook his head, blocking out Cas’ protests. “I’m sorry, Cas, you’re just gonna have to wait for something else to come along.”

Dean knew he was being harsh but it was for the best. Sirens were dangerous, way too dangerous for a rookie hunter on his first case, way too dangerous for… well, ok, probably not dangerous at all for an angel, even an angel that was on the tail end of falling, but even if Cas still had some angel mojo bottled up in there, that was no reason for him to go risking his life chasing down some shapeshifting mind controlling stripper bastard. Especially not after what happened the last time Dean got tangled up with one. No, they would take a pass on this case, thank you very much, and Dean wouldn’t examine why the idea of Cas going near a siren made him so especially uncomfortable, and then they would all move on with their lives, and that would be that.

He grabbed his laptop back from Cas and pulled up the Mothman article again.

Cas side-eyed him and hunched his shoulders up huffily.

“You know, that so called Mothman sighting is much more likely to be a fairy that’s gotten itself displaced,” he said dismissively.

Dean heaved a huge sigh. “Yeah, that’s what I was thinking. Dammit.” Cas tilted his head and squinted at Dean. Dean quickly backpedalled: “Oh man, uh, Sammy’s gonna be so disappointed. You know, that it isn’t actually Mothman. Yeah, that kid’s been dying to get a glimpse of him ever since he caught one of those history channel movies about it.”

Cas smiled. “What was the program called?”

“‘ _Unsolved Mysteries_ ’. It was this documentary series on Lifetime, actually- uh, I mean.” Dean coughed. “I dunno Cas, how the hell would I remember some random thing Sam watched fifteen years ago?” Dean scoffed, rubbing his neck.

“Indeed.” Cas said. He watched Dean scroll sulkily through the article for a minute before asking, “why don’t we see what Sam thinks about the siren case?”

At that Dean mustered a smug grin. “You know, I think that’s a great idea, Cas!” Sam could tell him just how bad an idea going down that road was, way better than Dean could articulate.

* * *

 

“I think that’s a great idea, Cas!”

Dean glared at his brother as he enacted possibly the most heinous act of betrayal Dean had ever been subjected to.

“Thank you, Sam. It really means a lot to me to have my ideas validated.” Cas shot Dean a smirk.

Dean sat aghast, both horrified that his brother and his- and Cas were teaming up against him in this way when he was clearly in the right, and dismayed that half of him could only focus on that cheeky smile on Cas’ face. The horror won out, in the end.

“I can’t believe you're enabling him like this.”

Sam laughed, the bastard. “What? I really do think it’s a good idea! Cas hasn’t had a chance to take the lead on a case yet and this is the perfect opportunity. Look how close it is to home! We’ll be done before dinner.”

Dean grumbled something under his breath.

“I’m sorry, what was that?” Sam struggled to hold back a smile.

Dean growled out, “I said, fine, as long as we’re back in time for the premiere.”

Sam’s struggle became even more futile. “The premiere? What premiere is that, Dean?”

Cas, of course, chose this moment to chime in. “Oh that’s right, the new season of Dr. Sexy starts tonight, doesn’t it Dean?” He supplied helpfully.

“Yes! Cas! Thank you!” Dean spat.

“I’m sure we’ll be back in time for it, but couldn’t you just record it to be on the safe side?” Cas asked.

“No, I can’t, those fuckin’ things never do it properly.”

Sam’s mouth looked like it was trying to turn itself inside out. Dean took great offense at this.

“They don’t, Sam! They either fuck up completely and like, record the wrong channel, or they only catch the first two thirds of the show and cut off the last twenty minutes! Those are the most important minutes!”

Cas nodded sagely. “The denouement is usually where the most relevant action happens in fictional media.”

Sam was straight up laughing now. Dean dropped his arms back to his sides from where he’d thrown them up in agitation. How was his life this shitty?

* * *

 

The boys all gathered round the table in the War Room. Dean, who had posted himself up in the corner leaning against the wall, was still determined to contribute as little as possible to the case - his small way of protesting the whole exercise - but that didn't mean he was gonna sit out the planning session altogether.

Cas settled himself at the head of the table, the better to dictate actions from, and Sam was back to trying to hide his amusement at the whole situation.

Like, for god’s sake, he got whammied by the last siren too! Why wasn’t he more concerned about this?

Cas cleared his throat and looked down at the notepad he’d been using to keep abreast of the case.

“Tyler Sheffield, the man from the article, lived only a few blocks walk from a local, very popular drinking establishment called Chuck’s Bar. This, of course, wouldn’t be much to go on as an isolated fact, but, from what I could tell, there have been several other cases similar to this one of spouses attacking their partners only to instantly express regret, and all of those people either live similarly close to this bar, or they were known to frequent it.”

Dean crossed his arms. “Ok, so they all liked the same bar. Sirens get their rocks off impersonating strippers and pole dancers, what’s this bar got to do with that?”

Cas frowned at the interruption. Dean, to his internal and eternal dismay, found it adorable, but that thought was quickly squashed by his annoyance at Cas for actually having an answer to his question.

“The theory is that sirens choose their hunting grounds based on easy access to their preferred prey. Of course, this means that the most common choices are strip clubs and the like, but it occurred to me that working at a bar would also offer up many similar opportunities. As I understand it from multiple examples in popular media, bartenders are often suppositories for people’s woes and insecurities about their personal lives. Additionally, it would be very easy for a siren to enthral a victim if they were to serve them drinks spiked with their venom. I believe as much happened to you on your last encounter with a siren, didn’t it, Dean?”

Sam jumped in before Dean could get rightfully worked up about it. “You sure have put a lot of thought into this, Cas. Good job!” He smiled encouragingly, then not-so-subtly glared at Dean, imploring him to do the same.

Dean, after shooting daggers Sam’s way for daring to continue this charade, relented, deigning to humour Cas by asking: “So, do you have a plan of attack, hotshot, or are we just rushing in and hoping it doesn’t kill us straight away?”

Cas scowled. “Yes, Dean, I did in fact spend a small amount of my time coming up with a better plan than ‘charge in and hope for the best’.”

“Why don’t you tell us what the plan is, Cas?” Sam’s prior amusement was quickly giving way to discomfort as he sensed the storm that was brewing between the two men he sat next to. Served him right for letting this get as far as it had.

“Thank you, Sam, I believe I shall.”

Dean rolled his eyes.

Cas studiously ignored this. "I decided that the best course of action would be for us to go to the siren's hunting grounds and provide the incentive for it to deliver itself into our hands. If all goes well, it will lead us to its lair and we can kill it discreetly, while also making sure it's not keeping any live victims."

Dean faked a yawn. "So you wanna run a honey trap?"

"Yes Dean, if I were to over simplify what is bound to be a very delicate operation, that's exactly how I'd do it."

"And who exactly are you gonna send in as bait?" Dean leaned back smugly. It was obvious where this was going, and as determined as Cas was to take point, he wouldn't actually force Dean to put himself in danger like this-

"Naturally, I will be the bait."

Dean's satisfied expression dropped off his face like it had been pulled down. "What?! No, nu-uh, nope, absolutely not."

Sam decided now would be an apt time to try playing mediator. "Dean, really... "

An apt time it was not.

"Shut your pie hole, Sammy!" Dean turned back to Cas. "You can't be serious. You wanna, what, walk right in there with your tax accountant trench coat and a can-do attitude and let this thing put the whammy on you?"

"I am not some unsuspecting mark, Dean. I am an angel, in case you have forgotten."

"Like I _could_ forget." Dean huffed.

Cas stood up and turned to face Dean fully. " _And,_ as an angel and not an emotion filled, irrational, overreacting human, I am the obvious choice to play bait for this case."

Dean decided it would best for everyone involved if he blew right past how that statement cut into him. It was time to put an end to this whole facade. "Look, I've indulged you this much-"

Cas cut him off. "Oh is that what you’ve been doing? Indulging me? It sure as hell looked like you were vacillating between sulking in the corner and trying to undermine me at every turn!"

Dean spluttered, flailing his hands. "Sulking? I'm- I was not- and _undermining_ is a strong word-"

Cas got right up in his face. "It is an entirely accurate term as that is what you’ve been doing ever since I brought this up. If you had this much of a problem with me being a hunter you should have said it to my face. Passive aggression doesn't look good on you."

Dean had never seen Cas sneer before. It was...

Dean swallowed hard and gave back as good as he was getting in the lean-close-to-intimidate department. "I don't have a problem with you hunting. What I've got a problem with is you being all gung-ho and charging in without thinking about what you're doing!"

"I'm not thinking? You're the one who wants to ignore a case because you can't handle not being in charge!"

Dean breathed hard, meeting Cas' gaze. They were standing so close now Dean could feel Cas' breath on his face.

“You can’t fight in here, this is the War Room!” Sam blurted out.

The tension in the room drained like a punctured fuel tank.

Dean turned slowly to look at Sam.

Sam's smile was a little manic. "You know? Dr. Strangelove?"

Dean shook his head and went to sit down, while Cas just looked lost.

“Cause, you know, the-“ Sam’s nervous chuckles trailed off and he screwed his face up. “Whatever, you guys don’t get classical humour.”

“God, you’re such a nerd.”

Dean didn't know why Sam looked so pleased with himself. It wasn't until they were in the Impala and on the way to Chuck’s Bar that he realised how artfully his little brother had defused that conversational bomb.

* * *

 

Dean had parked himself in the deepest corner of the darkest table at the farthest end of the room from the bar, a vantage point he had chosen to watch Cas from. Oh, and also he needed to make sure he saw who the siren was.

He’d ordered the cheapest beer they had and nursed it for the better part of an hour, scaring away any wait staff who dared approach him with a very dark expression that hadn’t lifted from his face since they arrived in this shitty town. Which was probably why he hadn’t been asked to order more drinks, or at the very least to stop taking up an entire table for himself. The bar wasn’t at capacity though, so Dean figured they had no reason to complain. Yes, Dean was in a bit of a bad mood, and it was only souring further the longer he had to watch Cas flirt with everyone he interacted with. It didn’t matter that he was so bad at it he ended up confusing people into ending the conversations more often than not. The point was that he was doing it at all. Dean had been paying attention to Cas’ lecture, no matter how hard he’d tried not to, and Cas had said that the bartender was the most likely suspect. Ok, sure, it made sense to explore all options; maybe the siren just used this place to chat up dudes, whatever. But Dean wasn’t in the mood for logic. He was in the mood to get this fucking case over and goddamn done with.

Cas finished yet another drink as yet another woman walked away from him. Dean didn’t celebrate even a little bit. Because he was a professional, and there would be no cause for celebration until the siren had been well and truly ganked. He watched as Cas caught the attention of the bartender. She smiled at him and pointed behind her at someone just entering the bar from the kitchen. The new woman nodded at the bartender and went over to Cas, picking up an empty glass as she went. Dean sat up straighter.

Ok, he thought, new bartender just started her shift. Could mean nothing, could mean that the reason Cas hasn’t been sirened up until now is because the siren hadn’t been in the bar…

Cas finished ordering his drink and the woman leaned under the bar to grab it- there. Dean craned his neck as far as he could without looking completely suspicious. She definitely could have spat in the drink while her head was down behind the bar.

Dean shifted back deeper into his booth seat to get a better angle on Cas, trying to catch the moment he took a drink from the glass.

“Ok man, I’m sorry, but I really am gonna have to ask you to leave this time.” A waiter walked up to Dean’s table, standing right goddamn in between him and the bar, blocking his view of Cas entirely.

Dean threw himself to the side, almost lying down on the seat, straining to catch a glimpse of Cas, of the siren, of the poisoned glass.

“Dude, seriously, I was gonna let you go - it looked for a second there like you were about to get up - you can’t take up a whole table all night.”

Dean leapt up out of his seat and shoved the guy to the side. “Yeah, whatever, can you get out of my way for a fuckin’ second?”

The kid’s imploring expression turned serious. “Sir, I’m going to have to ask you to leave now.”

Dean ignored him, searching the bar frantically for any sign of a tan coat, a shock of black hair, a pair of bright blue eyes-

“Don’t make me get the bouncer!”

Dean turned to face the waiter and whatever the kid saw on Dean’s face shut him right the hell up. Dean pushed past him, hand already on his gun; it was taking the last of his willpower not to pull it out right in the middle of this very public place.

He ran up to the bar, where a small crowd of disgruntled patrons was now gathering. The bartender was nowhere to be seen and people were getting impatient, yelling their drink orders louder and louder as if that was gonna get them anywhere. Dean shouldered his way to the front of the bar and shot a last, hopeful look up and down the length of it. Nothing.

Cas was gone.

He slammed his fist down in frustration, causing a few of the people nearby to yelp, and headed to the door, pulling his phone out as he went.

It rang over and over as Dean headed to the Impala.

“Dean?” Sam pulled his headphones out of his ears and climbed out of the driver’s seat.

“It got him.” Dean brushed past Sam and got behind the wheel, starting the car. Cas’s voicemail message started playing in his ear, so he lobbed his phone into the back seat. He barely waited for Sam to scramble around to shotgun before peeling out of the parking lot.

“The siren-?”

“It got Cas and I lost eyes on him and I have no fuckin’ idea where it coulda taken him.”

“But I didn’t see them come out; I’ve been watching the door since you guys went in.”

“They must have gone out the back door, Cas was right, it was working as a bartender.”

“’Must have’? You mean you didn’t actually see where they went?”

Sam startled as Dean slammed his hands on the steering wheel. “No, I didn’t see where they fucking went, ok? This fucking waiter got up in my face, and by the time I shook him off Cas had drunk the fucking poison and he was gone.”

Sam just watched as Dean breathed hard, and jumped again when he yelled suddenly. “Idiot! That goddamn stupid son of a bitch!”

“Dean…” Sam cut himself off as Dean careened the car around a corner way too fast.

“Why did he drink it? He _knew_ it was poisoned - I was sitting a fucking mile away and I could tell that much - so why did he drink it? How is he gonna stand up against a monster when it's got its goddamn hooks in his brain? Why would he be that fucking _stupid_?”

Sam treaded lightly. “We need the blood of someone infected with the siren’s venom to kill it. Cas is nothing if not practical when it comes to monsters. He was probably relying on us to follow him after he got infected so we could use his blood to kill it.”

“Yeah, well, then he’s an idiot for trusting us, too! Look where that’s gotten him!”

“Dean…”

Dean sent the Impala screaming around another bend in the road; they were definitely violating traffic laws at this point. “I knew it, I always knew we were just dragging him down. He trusts us to take care of him this one time, and what happens? I get held back by a fucking hundred and forty pound kid in an apron and just let some fucking _creature_ come and scramble his brain.”

Dean’s knuckles shone white against the black of the steering wheel.

Sam pulled out his phone and started fiddling with it. “Where are we going?”

“I don’t know Sammy, not for sure, but if the siren keeps coming back to this same bar it probably set up its lair nearby it, right? So I’m gonna just keep circling this area, get further from the bar as we go, try and keep an eye out for any, fuck, I dunno, any obviously abandoned buildings, or warehouses, some shitty dingy train station, fuckin’ anything that looks like some scum-of-the-earth parasite would use as a hideout. I mean, fuck, maybe we’ll get lucky and see Cas in the back of some pick-up truck, or we’ll see them heading into one of these houses, or, or..." He laughed helplessly. “I don’t know! I don’t know where he went, where it took him, where it took him to suck the life out of him. I have no goddamn idea where they could have gone but I can’t just fucking _sit here_ and wonder, Sam, ok? I have to do something, I have to keep moving, and trying to find him, or I’m gonna lose my goddamn mind.”

Sam stopped tapping at his phone. “Dean.”

“What?”

“Take the next left.”

Dean whipped his head around to stare at his brother. “What?”

Sam started to answer, then stopped to grab the wheel and straighten it before they could crash into an oncoming car. “Jesus Christ Dean, I know you’re freaking out right now but pay attention to the road, please. Literally for both our sake’s.”

Dean stared back out the windscreen and calmly turned left at the intersection.

“Ok, and take a right up at the next set of lights.”

Dean growled. “I swear to god, Sammy-“

“Like I said, I know you’re freaking out, but really, dude. Come on. Find My Friends is like, a free app.”

* * *

 

Dean hadn’t actually been too far off the mark. Sam tracked Cas’ phone to a dilapidated old building about ten blocks from the bar. From the outside it looked like the place had been empty for years; nature was reclaiming the garden and was in the middle of making a frontal assault on the house itself.

Dean thanked God and Kali and all the other deities they hadn’t killed yet that his little brother was pedantic enough to go and install a tracking app on all their phones without mentioning anything to him, because if it weren’t for that they’d have no reason to suspect this house over the other similarly shitty ones they’d passed in the time since they’d left the bar.

He parked the Impala around the corner from the lot, and with a nod to Sam they both moved quietly up to the side of the house. Sam jerked his head towards the back of the building, waited for Dean to nod in reply, and headed that way. Dean, gun firmly in hand, crept up to the front window. The lacy white blinds that once hung in it had fallen halfway down, leaving Dean with a triangular area through which he could just make out two figures moving inside. That was good news. They hadn’t come across any accounts of sirens working in packs, but now definitely wasn’t the time to start getting lazy and making assumptions.

Dean watched as the figures moved towards each other. And kept moving. They were almost touching now.

Dean kicked the door down.

Cas and the siren stood in front of the couch in the front room, standing so close to each other it made Dean’s skin itch. The siren, still wearing the skin of some gorgeous generic blonde, had one hand on Cas’ chest, the other cupping the back of his neck. They were leaning slowly into a kiss. Dean’s brain short circuited.

“Get the hell away from him!” He snarled, levelling his gun at the siren’s head.

It froze for a second, face inches away from Cas’, then turned slowly to look at Dean, body stiff, no sudden movements.

Then it caught sight of the gun and its whole body relaxed.

“Oh, okay, guns. I can deal with guns. Guns are like, not even a thing- is this your first rodeo or something, hunter?”

Dean growled under his breath and switched out his gun for a bronze knife. Behind the siren, Cas stiffened.

The siren looked a little less cocky for a second. “Ok, maybe not as green as that. But you’re still kinda at a disadvantage here.”

“Oh yeah?” Dean ground out.

The siren smirked. “Oh, yeah. I mean, what are your options here, exactly? You could… come close enough to me to stab me but risk me getting all up in your brain stem. You could wait for the backup you surely have coming, and see if he’s better at this whole gig than you are, or you can try and go for- I’m sorry, honey, what was your name again?”

The siren turned its attention to Cas briefly.

He gazed back at it with an adoring expression. “Cas.”

It flicked its hair over its shoulder and looked back at Dean. “You can try and go for Cas here, get him out of harm’s way or whatever but, sweetie, I don’t think he’s gonna make it easy for you. Isn’t that right, love?”

Cas shook his head, still looking spacey. Dean swallowed back bile.

“Listen to me you fucking parasite-“

The siren rolled its eyes. “Baby, grab that knife off him, won’t you?”

So fast Dean didn’t register it until it was over, Cas stepped forwards and disarmed him.

The siren laughed beatifically and did a little twirl around Cas, landing behind him with its hands around his waist and its head cheek to cheek with his in a faux imitation of an embrace. “In fact, if you don’t tell your cavalry to get in here right now and lay down their weapons, well, then Cas here is gonna be real upset. Just, just completely broken up inside. So much so that he might just lose the will to live.” It feigned a sob, hiding its face in its arm melodramatically before lifting back up to shoot Dean that arrogant, static smile. “And we don’t want that, now, do we?”

Dean watched with disgust as the creature whispered something in Cas’ ear, nuzzling at his hairline as it did.

The disgust morphed instantly into terror when the siren finished and Cas lifted the bronze knife to his own throat.

“Call. Off. Your. Dog.”

Dean swallowed hard. “Sam!”

The door on the other side of the room opened slowly and Sam walked in, arms held out, palms up.

“Over there, stand next to him.”

Sam nodded placatingly and moved slowly to stand by Dean. He started to lower his hands.

“Cas!” The siren barked.

Cas pressed the knife harder into his own skin. Sam froze.

Dean’s eyes were glued to the blade of the knife, only seconds and a few pounds of pressure away from spilling blood.

“Cas…” he choked out.

The siren tilted its head, that fucking ever-present smile finally giving way to a puzzled frown as it took Dean in.

“Oh. Huh.” It leaned back thoughtfully and tapped a finger on its chin. “So that’s what that is.”

Dean didn’t take his eyes off Cas’ throat. “What? That’s what what is?”

The siren stared into space for a beat, then shook whatever thought it’d had loose. “Oh, nothing, I’ve been getting this weird impression from you. I just figured out what it was.” It shrugged happily. “Lucky, huh? Not knowing that was gonna annoy me, like, for the rest of the week.”

Dean’s mouth felt like it had been caulked up. Sam must’ve deduced as much. “Look, if you let our friend go, we promise we won’t come after you.”

This time there was a real cruel edge to the siren’s laugh. “Oh, you’ll _let_ me go? Oh how _generous_ of you! Because, it’s not as if I’ve got the upper hand, is it? No, no, you boys are doing such a good job, really it would be in my best interest to let him go and save myself from all the peril I’m facing, is that it?” The creature leaned its elbow on Cas’ shoulder and covered its face with its hand as if to stay the laughter. “Wait, I’ve got it. You have a _secret weapon_ , something that I couldn’t possibly see coming, something that in a hundred years of hunting my kind, you hunters have now only just discovered!” The creature laughed like it was choking. Dean wished it would.

The boys waited for the hacking noise to die out, eyes flickering between the siren and its prey. It walked towards them after it finally stopped cackling. “Yeah, not so much. He’s in my thrall, nice and deep, and clearly you _both_ ,” the siren looked pointedly at Dean, “care a great deal about him. You’re not gonna risk his life just to stop little ol’ me, and I’m not gonna give up the best leverage I have. All the facts point to you letting me be on my way!”

It walked back over to Cas, turning its back on the brothers in a confident dismissal. “Now if you’ll excuse me, I think me and my boy here are gonna-”

As soon as it touched him, Cas drew the blade from his neck and stabbed the siren in the chest.

Dean wasn’t one for clichés, but hell if time didn’t slow to a fucking stand-still.

The siren was the first to break the spell. Dean would’ve said it shrieked like a banshee if he didn’t know what a real one sounded like. It shrieked a horrible shriek and fell to the floor, scrabbling desperately at the knife embedded in its sternum.

“How…?” it managed to garble out.

Dean, understandably, had a similar question in mind.

“I… saw you… drink from the glass… my venom.... I was so… sure…”

Cas just looked down at it for a second before pulling the knife out, and the creature was silent.

If Dean didn’t get any fucking answers he was gonna lose his goddamn mind.

Sam was the first to speak up. “Damn, Cas, you sure had us going! That must’ve been some smooth as hell sleight of hand for you to trick the siren. She had to’ve been watching you closely, right?”

“Oh, no, I did drink the poison.”

For the second time in as many minutes, Dean felt time screech to a stop. At least, it started to, until Cas decided to say something even more bat-shit.

“I’m afraid I have to apologise to the two of you.”

It was at that point that Dean noticed the trail of blood on Cas’ neck. Cas noticed him staring.

“Right, yes. I had to cut myself, at least a little bit, to get my infected blood on the knife.”

Sam interrupted what was definitely gonna be Dean asking a reasonable question and not just screaming in confusion. “Cas… how did you overcome the thrall? I’ve been under it, we both have.” He gestured to himself and Dean, then huffed out a laugh. “I mean, shit, I had an easier time resisting Lucifer!”

Cas nodded, looking a little ashamed. “I promise you, I really had intended for this case to be a fair test of my readiness to take the lead on hunts. That’s why I volunteered to be the bait; it was only fair that I throw myself into the shallow end.”

“Deep end.” Dean croaked out.

Cas tilted his head to the side for a second, then nodded and continued. “And that’s also, well, one of the reasons why I drank the venom. I wanted to fully embrace my role. And, of course, I had all the faith in the world that you two would find me.” He smiled at them. He trusted them so damn much. Dean’s chest hurt.

“Plus I am still part angel, so a bronze knife wouldn’t have killed me, the risk was minimal.”

Sam nodded. “So she couldn’t tell you were an angel?”

“No. Otherwise we most certainly wouldn't have gotten this far.”

“Yeah, what a damn shame that would’ve been,” Dean threw in.

Cas ignored him. “But really, I do need to apologise to you both. This wasn’t, technically speaking, a fair test.” He frowned. “Well, it was more of a Schrodinger's cat situation up until I drank the venom. I didn’t know for sure that it wouldn't work on me. But I did suspect, so I apologise for deceiving you.”

Dean shook his head. “Wait, wait. You thought the venom wouldn’t work on you? What, cause you’ve still got grace?”

“No, my grace really only serves to protect me from mortal damage at this point, as well as giving me more strength than a regular human. Besides, there have been instances in the past of sirens enthralling angels. You do _not_ want to hear how those turned out.” From the look on his face, Sam kinda did.

Cas soldiered on. “My reasoning was much less metaphysical than that. And,” here Cas squirmed a little, “I must further admit that my main reason for drinking the venom, and indeed for choosing this particular hunt, was because I wanted to know if I was right about this. I’m not sure how valuable this information will be to the larger hunting community, but knowledge for knowledge’s sake has always been considered a noble cause-”

“Cas, buddy, please stay on topic. I’m begging you.”

Cas took in Dean’s appearance, noticed how confused and desperate he was, how he was just barely keeping all this in check, and relented.

“I understand the terminology for what I’m doing is to ‘come out’?”

Slightly. He relented slightly.

“What? I… what?” Dean didn’t have the first fucking clue what this had to do with Cas drinking goddamn siren venom.

Sam looked between Cas and the siren, who now appeared to just be a dead woman lying on the floor, and something apparently clicked. He turned his gaze on Cas and asked, with some confusion, “So, you’re gay?”

Cas shook his head. “I’m asexual.”

Sam’s expression cleared. “Ohhhhh. That explains a lot,” he muttered under his breath.

Dean wasn’t so sure that it did. “Asexual? Like, a- meaning ‘without’? So, ‘without’ sexuality?” Sam didn’t have to look so goddamned surprised, they spend half their time reading shit out loud in Latin, why wouldn’t Dean have picked up a thing or two?

Cas looked inordinately pleased. “Yes, that’s right! It has been adopted more colloquially to mean someone who does not experience sexual attraction, but that is the general gist of things.”

Dean, still having some trouble with this sudden left turn in the conversation, did what he seemed to do best around Cas, and brought up the past. “I thought you were, uh, ‘utterly indifferent to sexual orientation’.”

Cas raised one eyebrow, the sarcastic bastard. “It occurred to me that that was a rather dismissive attitude, you know, after I stopped trying to be literally God.” He shrugged. “I did some research. You know, there really is quite a lot of information about human sexuality online, it’s difficult to know where to start...”

Dean phased out as he saw a sudden, incredibly vivid image of Cas reading everything on the internet that had to do with sexuality, head tilted and eyes squinting in bemusement… Oh god, he definitely watched a bunch of weird porn, right? Dean managed to pull his head back into the game before that thought could go any further and caught the tail end of Cas’ speech, coughing to hide his fluster.

“-so I am now much better versed in the many nuances of human sexuality. This is the one that best suited me. It's very refreshing to have a name for it.”

“Yeah, I imagine it must be, very refreshing, right, Dean?” Sam said with a look that Dean could tell was meant to be heavy with some form of meaning.

“So why did it look like some generic hot chick then?” Dean asked.

Sam shrugged. “That’s like, a siren’s MO, isn't it?”

“Well, not really, they’re supposed to look like your ultimate sexual fantasy.”

Sam’s eyes widened slowly. “You know what Dean, you’re right. They are supposed to look like your ultimate sexual fantasy!”

Dean wasn’t at all comfortable with how enthusiastically Sam was agreeing with him but pushed that thought aside for the moment. “But, Cas, from the sounds of it, you don’t really have that? So what gives?”

Cas looked down at the dead creature. “My best guess would be that, upon failing to find any appropriate image in my mind to base itself on, the siren fell back on a form that had worked well for it in the past.”

Sam shook his head. “Yeah, but why a woman? You could’ve been gay for all it knew.”

Dean had an answer. “Heteronormativity.”

All eyes turned to him.

He crossed his arms. "What? I read, I know shit.”

This, from the looks on their faces, wasn’t explanation enough.

Dean huffed. “I- There's a lot of intense analysis of this kinda stuff online! Ask Cas, he obviously knows. And- I’m a hunter, we like to have, terminology- you wanna know what people are saying, and if a certain word comes up a lot- and it’s interesting! A lotta stuff’s changed since the last time I-”

Sam, good old Sam, reliable Sam, interrupted Dean’s monologue before it could get really out of hand. “But Dean, didn’t you have a male siren?”

Sam, his piece of shit little brother, Sam who didn’t know when to keep his goddamn mouth shut, continued on in blissful ignorance of the metaphorical blades Dean was precision firing in his direction. “Hey, Cas, did we ever tell you about Dean’s siren, and how it was a dude?”

“Well, _obviously,_ ” Dean ground out. “They aren’t infallible. Look how wrong they got Cas.”

“Cas is an angel. And asexual.”

“Moving right along-”

“I’m just saying, if this siren defaulted to a female form as its best guess when it couldn’t read Cas, why was yours a guy? And, actually, that one should’ve been able to read your mind fine, you’re just a human and no matter how much demony bullshit has happened to you in the meantime, you _definitely_ were back then, so…”

Dean took in Cas’ well-meaning smile and his brother’s completely unsubtle smug grin, seized the reins of the conversation and violently changed track. “Look, let's just deal with the siren, ok? The reason we’re here in the first place? Do our jobs? If you guys don’t mind?”

“Dean, the siren is dead; my poisoned blood on the bronze blade killed it. You were here for that,” said Cas.

“Yeah Dean,” said Sam, the traitor. “The siren is dead, the day is saved, and we’ve got nothing else to do today. Let’s really get into this topic of discussion; I’m so interested in your take on-”

Dean turned on his heel and left the room, muttering something about cleaning up the evidence they left at the hotel room. He didn’t leave fast enough to avoid overhearing the next few things to come out of Sam and Cas’ mouths, though.

“You booked a hotel room this close to the bunker?”

Dean could _hear_ Sam’s grin. “Nope.”

“Then where is he going?”

“I think he’s just flustered,” Sam lied, the liar.

“He’s probably worried the DVR missed the ending of the Dr. Sexy premiere.”

Dean scoffed to himself at how skewed a view those two had of his priorities, and climbed into the Impala.

* * *

 

The DVR, as it turned out, had cut out the recording at the exact moment Dr. Sexy was about to find out if his ex-wife had woken up from her coma. Dean carried it all the way up the stairs of the bunker just so he could throw it out a window.

 

**Author's Note:**

> You know there actually is a bar in Salina, KS called Chuck's Bar? How could I pass up such an opportunity?


End file.
